1. Field of the Invention
The present invention relates to a recording-media tape reel with disc flanges at the upper and lower ends of a cylindrical hub having an outer periphery on which tape is wound.
2. Description of the Related Art
Magnetic tape is used as recording media that are employed in an external storage unit for computers and other recording-reproducing units. The magnetic tape is wound on a tape reel and housed within a cartridge case. If the magnetic tape cartridge is loaded into a recording-reproducing unit, rotation of the tape reel causes the magnetic tape to run, and recording or reproduction of data relative to the recording surface of the magnetic tape is performed.
Recent magnetic tape has a large capacity and can store up to tens to hundreds of G bytes per reel. To realize this large capacity, a pitch between data tracks is narrowed, or tape thickness is made thin, or servo signals are written in. For this reason, the tape running mechanism of a drive unit and the cartridge structure are required to have high precision. Particularly, the precision of a reel configuration on which magnetic tape is wound is required to be high.
The above-mentioned tape reel is constructed of a cylindrical hub with its center line as an axis of rotation, and a pair of disc flanges extending radially from the upper and lower ends of the hub. Space for winding recording-media tape is formed between the outer periphery of the hub and the opposing interior surfaces of the flange pair. Generally, in the case where the tape reel is made up of resin-molded components, the lower flange and the hub are integrally formed and the upper flange separately formed is fixedly attached to the upper end of the hub.
The fixed attachment between the hub and the upper flange is usually performed by an ultrasonic welding method, using weld bosses or an energy director. The ultrasonic welding is being widely used for manufacturing tape reels, because it shortens manufacturing time, and because it uses a portion melted from a molded component as a binder and therefore reduces the running cost.
If, in a magnetic tape cartridge with such a tape reel, the interior surface of the flange being rotated makes contact with magnetic tape, there is a possibility that the problem of damage to the magnetic tape or dust occurrence will arise. This problem becomes a more important consideration, as recording density in the magnetic tape becomes greater, and as higher reliability is needed. Particularly, if the thickness of the magnetic tape (including a magnetic recording layer) is reduced to 20 xcexcm or less, particularly 15 xcexcm or less, damage to the magnetic tape due to the aforementioned rubbing will become conspicuous.
In view of the circumstances mentioned above, it is a first object of the present invention to provide a recording-media tape reel that is capable of preventing recording-media tape such as magnetic tape from making contact with the interior surface of the flange.
The aforementioned magnetic tape cartridge, incidentally, is divided into a one-reel type and a two-reel type. For example, a drive unit, which drives a one-reel type of tape reel, has an annular driving gear and a magnet at the top of a rotating shaft so that a chucking operation with the tape reel can be reliably performed. The drive unit is constructed such that the driving gear meshes with a reel gear formed in one end surface of the tape reel and drives the reel gear without play between them.
In the case where the tape reel is driven by the engagement between the driving gear and the reel gear, the chucking operation can be reliably performed, but it is fairly difficult to form both gears precisely. Therefore, when the tape reel is being rotated by the engagement between both gears, there is a slight surface runout in the radially outer ends of the upper and lower flanges of the tape reel, and therefore, the radially outer end of the flange is moved toward or away from the magnetic tape being unwound from the tape reel.
Thus, if there is surface runout in the engagement between the driving gear and the reel gear, a slight runout will occur in the rotation plane of the reel gear perpendicular to the rotation center of the driving gear, and surface runout at the radially outer end of the flange due to the influence will be increased. Furthermore, if the surface runout that the tape reel itself has because of low molding precision, etc. is added, a greater surface runout will occur.
On the other hand, the high precision of the position at which magnetic tape runs is required in order to assure the reliability of the recording-reproduction characteristics of the magnetic tape having the aforementioned high capacity. The high precision of the flange position is also required, because there is a possibility that if surface runout in the flange become great, the flange will make contact with magnetic tape and have a great influence on tape running precision.
However, there are cases where for engagement precision between the driving gear and the reel gear and the molding precision of the tape reel, it is difficult, from the viewpoint of mass production, etc., to assure sufficient precision to meet enhancements in recording density and recording precision.
Therefore, a second object of the present invention, in a recording-media tape reel equipped with a reel gear which meshes with a driving gear and is rotated, is to eliminate the influence of the flange on tape running and assure satisfactory recording-reproduction characteristics, even when there is surface runout in the tape reel being rotated.
To achieve the first object of the present invention mentioned above, there is provided a first recording-media tape reel comprising:
a cylindrical hub with its center line as an axis of rotation; and
a pair of disc flanges extending radially from upper and lower ends of the hub so that space for winding recording-media tape is formed between an outer periphery of the hub and opposing interior surfaces of the flange pair;
wherein H1xe2x88x92xcex1 greater than H2+xcex2 is met, when H1 is a reference value for a distance HIN from a reference plane, perpendicular to the rotation axis along an exterior surface of one of the two flanges, to a radially inner end of the interior surface of the one flange, xcex1 is a tolerance on a negative side of H1, H2 is a reference value for a distance HOUT from the reference plane to a radially outer end of the interior surface of the one flange, and xcex2 is a tolerance on a positive side of H2.
That is, the present invention is characterized in that the minimum value of HIN is always greater than the maximum value of HOUT. It is preferable that this condition be established at any position on the reel, when the thickness of the recording-media tape is 20 xcexcm or less, particularly 15 xcexcm or less, and furthermore, 10 xcexcm or less. The reason for this is that the aforementioned damage will tend to occur more easily, as the recording-media tape is made thinner. In addition, since thinner recording-media tape is used for high-density recording, damage will become a problem even when it is slight.
In the first recording-media tape reel, the one flange may be formed integrally with one end of the hub, and the other of the two flanges may be fixedly attached to the other end of the hub. In the case of such a tape reel, the upper and lower flanges are resin-molded components and integration of them is normally performed by ultrasonic welding, so there is a limit to the precision. Assuming xcex94H=HINxe2x88x92HOUT, xcex94H is not always constant at all positions along the radially outer end of the flange. Because of this, the aforementioned values of HIN and HOUT have tolerances, respectively, and manufacturing precision is managed so that the values of HIN and HOUT are within the tolerances. However, since it is obvious that it is more difficult, from the mechanical standpoint, to obtain the dimensional precision of the outer distance HOUT than to obtain the dimensional precision of the inner distance HIN, a tolerance for HOUT is set wider than that for HIN. Therefore, there are cases where there occurs, depending on the size of a tolerance, a reversed phenomenon that HINxe2x89xa6HOUT is obtained, not HIN greater than HOUT.
According to the first recording-media tape reel of the present invention, the minimum value of HIN, H1xe2x88x92xcex1, is always greater than the maximum value of HOUT, H2+xcex2. Therefore, the reversed phenomenon mentioned above will no longer occur. Even when recording-media tape is 20 xcexcm or less in thickness, the recording-media tape can be prevented from being damaged because of rubbing between the tape and the flange interior surface.
To achieve the second object of the present invention mentioned above, there is provided a second recording-media tape reel comprising:
a cylindrical hub with an outer periphery on which recording-media tape is wound;
upper and lower disc flanges extending from upper and lower ends of the hub; and
a reel gear meshable with a driving gear;
wherein, when the reel gear meshes with the driving gear and is rotated, a height of a radially outer end of the lower flange is at a position lower than a height of a radially inner end of the lower flange, and a height of a radially outer end of the upper flange is at a position higher than a height of a radially inner end of the upper flange.
In the second recording-media tape reel, the lower flange may be formed integrally with the lower end of the hub, and the upper flange may be fixedly attached to the upper end of the hub. In that case, it is preferable that t2 greater than t1 be met, when t1 represents a difference between the heights of the radially inner and outer ends of the lower flange and t2 represents a difference between the heights of the radially outer and inner ends of the upper flange.
According to the second recording-media tape reel of the present invention, when the reel gear meshes with the driving gear and is rotated, the height of the radially outer end of the lower flange is at a position lower than the height of the radially inner end of the lower flange, and the height of the radially outer end of the upper flange is at a position higher than the height of the radially inner end of the upper flange. Therefore, the upper and lower flanges have no influence on tape running, even if they are subjected to the influence of surface runout caused by the engagement between the driving gear and the reel gear. Thus, since satisfactory running precision is assured, recording-media tape meeting the high-density requirement can be used in the tape reel of the present invention.
In addition, the value of t2 for the upper flange is set greater than that of t1 for the lower flange (t2 greater than t1), because the amount of surface runout of the upper flange is basically greater than that of the lower flange near the reel gear.